Purely absorptive three-dimensional infrared spectroscopy.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Chemical Physics

Background:

• Vibrational spectroscopy provides insights into molecular dynamics.
• Three-dimensional (3D) fifth-order vibrational spectroscopy offers a detailed probe of anharmonic couplings and energy transfer pathways.
• Experimental determination of 3D spectra, especially absorptive components, is challenging.

Purpose of the Study:

• To demonstrate a novel method for collecting purely absorptive 3D fifth-order vibrational spectra.
• To characterize vibrational energy transfer in a model system (CO2 in H2O).
• To validate the experimental method through comparison with theoretical simulations.

Main Methods:

• Utilized a six-beam interferometer setup for 3D fifth-order vibrational spectroscopy.
• Developed and applied a method for experimentally determining the phase of the 3D spectrum.
• Employed the cumulant expansion theory for spectral simulations.

Main Results:

• Successfully collected purely absorptive 3D fifth-order vibrational spectra of CO2 in H2O.
• Identified five distinct peaks corresponding to different vibrational energy transfer pathways.
• Observed excellent agreement between experimental spectra and cumulant expansion simulations.
• Demonstrated linear scaling of peak intensities with concentration.
• Confirmed negligible contribution of cascaded lower-order signals.

Conclusions:

• The developed method reliably provides purely absorptive 3D fifth-order vibrational spectra.
• The experimental results align with theoretical predictions, validating the cumulant expansion approach.
• The study elucidates vibrational energy transfer dynamics in the CO2/H2O system.